Field
The present invention relates primarily to a process for producing phosphinates (phosphonous acid monoesters) of the defined formula (I) below and use thereof for producing biologically active substances which may be used in the pharmaceutical or agrochemical sector, preferably for producing phosphorus-containing amino acids.
Description of Related Art
Phosphinates (phosphonous acid monoesters), alkyl phosphinates for example (alkylphosphonous acid monoesters), are valuable intermediates in various industrial fields, in particular for producing biologically active substances which can be employed in the pharmaceutical or agrochemical sector.
U.S. Pat. No. 4,168,963, for example, describes a wide variety of phosphorus-containing herbicidally active compounds, among which in particular phosphinothricin (2-amino-4-[hydroxy(methyl)phosphinoyl]butanoic acid; common name: glufosinate, referred to hereinbelow as glufosinate) and the salts thereof have attained commercial importance in the agrochemical sector.

Methods for producing intermediates for the synthesis of such phosphorus-containing herbicidally active compounds, in particular of glufosinate, are described in U.S. Pat. Nos. 4,521,348, 4,599,207 and 6,359,162B1 for example.
The production of monoalkyl phosphinates is known to those skilled in the art and may be effected according to processes known from the literature, for example in accordance with U.S. Pat. Nos. 3,914,345; 4,474,711 or 5,128,495).
The production of monoalkyl phosphinates starting from particular halophosphorus compounds is described, for example, in U.S. Pat. No. 4,485,052, GB 1461 376 and GB 1 490 835.
The production of dialkyl alkylphosphonites is described, for example, in U.S. Pat. No. 5,166,385.
Furthermore, saponification reactions of certain dialkyl alkylphosphonites to give alkyl phosphinic acids or monoesters thereof are known, as described for example in Applied Spectroscopy 1968, 22, 95-98, J. Med. Chem. 1988, 31, 204-212, J. of General Chem. of the USSR 1962, 32, 3288-3296, Synthetic Communications 2003, 33, 1665-1674 and J. Organomet. Chem. 1997, 529, 135-142.
J. Am. Chem. Soc. 1958, 80, 5937-5940 describes the transesterification of certain dialkyl alkylphosphonites.
The processes from the prior art for producing alkyl phosphinates (alkylphosphonous acid monoesters) still have disadvantages however, such as insufficient purities and/or yields of alkyl phosphinates (alkylphosphonous acid monoesters), an excessive fraction of co-products or by-products, excessively complicated purification or isolation of the alkyl phosphinates (alkylphosphonous acid monoesters) and/or reaction conditions that are excessively difficult in terms of process or plant technology.
Alkylphosphonous acid mono-C1-C3-esters are preferably not used on an industrial scale due to their low stability and their hazard potential. In the large scale synthesis of glufosinate ammonium, therefore, butyl methylphosphinate is an important intermediate.